It is known that halogenated isoquinoline derivatives such as ripasudil (chemical name: 4-fluoro-5-{[(2S)-2-methyl-1,4-diazepan-1-yl]sulfonyl}isoquinoline) represented by the following structural formula:

and 4-bromo-5-{[(2S)-2-methyl-1,4-diazepan-1-yl]sulfonyl}isoquinoline represented by the following structural formula:

have pharmacological action such as Rho kinase inhibitory action (Patent Literatures 1 and 2, for example), and thus, are usable for the prevention or treatment of eye diseases. Specifically, for example, halogenated isoquinoline derivatives are reported to be suitable for prevention or treatment of ocular hypertension or glaucoma (Patent Literature 3, for example), for which reduction of intraocular pressure is effective.
Hence, it is extremely useful to establish a technique for producing stable preparations of these halogenated isoquinoline derivatives as ophthalmic agents, for example.